This grant is a K08 Mentored Career Developmental Award submission supporting the research of Dr. Sunjay Kaushal. To advance his career in stem cell based therapy for congenital heart patients, this grant incorporates training in two vital fields: (1) molecular biology techniques (isolation and characterization of cardiac stem cells, immunohistiochemistry) and (2) in vivo transplantation techniques. Both of these fields is absent from Dr. Kaushal's previous training, yet are vital in advancing research in this field. Dr. Kaushal's mentor is Dr. Doug Losordo at Northwestern University who has an extensive research experience in this field. Recent evidence has identified a population of cells within the heart itself as a potential autologous cell source for cellular regeneration, termed cardiac stem cells (CSCs). As of yet, the clinical application of these CSCs for pediatric patients who develop non-ischemic cardiomyopathies is unclear. To accomplish this objective, we will have three Specific Aims which follow a progressive sequence. Aims 1 and 2 center on the accrual of detailed descriptive properties of the growth, self-renewal potential, and myocardial differentiation characteristics of hCSCs from different anatomic sites of the heart. In addition, we will determine whether age or the pathologic state of the patient affects the innate properties of the hCSCs. The in vivo analysis will involve examining quantitative and qualitative myocardial regeneration in a doxorubicin-induced cardiomyopathy model, which replicates many of the salient features of cardiomyopathy present in our children with heart failure. Once we have established whether the human myocardium maintains a generic CSC or, in contrast, a more cardiac chamber-specific CSC, which may be influenced by age and physiologic state, we will test the best identified CSC to determine whether it is superior, inferior, or equal to bone marrow-derived cells for the regeneration of cardiomyocytes and coronary vessels in the doxorubicin- induced cardiomyopathy model. We strongly believe that elucidating these issues is critical to constructing the most powerful regenerative clinical protocol. RELEVANCE (See instmctions): Since all of the experiments in this proposal involve human tissues, there will be very strong translational conclusions that will directly impact the development of future clinical trials. Furthermore, these experiments have direct clinical applications to patients who have congenital heart defects as these patients are living longer, and some develop cardiac dysfunction that may benefit from a cell-based therapy using hCSCs.